Method and apparatus in video coding with flexible coding order

ABSTRACT

An apparatus includes processing circuitry, which determines a block vector that points to a reference block in a same picture as a current block in an intra block copy mode. The current block is one of a plurality of coding blocks in a coding tree block (CTB) with a right to left coding order being allowed within the CTB. The processing circuitry checks that two corner samples of the reference block have been reconstructed based on first outputs from a derivation process for block availability. The processing circuitry checks that a non corner sample of the reference block has been reconstructed based on a second output from the derivation process. The processing circuitry encodes the current block based on reconstructed samples of the reference block after a determination that the two corner samples of the reference block and the non corner sample of the reference block have been reconstructed.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. Ser. No. 16/844,058filed on Apr. 9, 2020, which claims the benefit of priority to U.S.Provisional Application No. 62/834,335, “REFERENCE SEARCH RANGEAVAILABILITY FOR INTRA PICTURE BLOCK COMPENSATION WITH FLEXIBLE CODINGORDERS” filed on Apr. 15, 2019. The disclosures of the priorapplications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 shows a schematic (201) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 3, a current block (301) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (302 through 306, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. For example, theprocessing circuitry decodes prediction information of a current blockfrom a coded video bitstream. The prediction information is indicativeof an intra block copy mode. The current block is one of a plurality ofcoding blocks in a coding tree block (CTB) with a right to left codingorder being allowed within the CTB. Further, the processing circuitrydetermines a block vector that points to a reference block in a samepicture as the current block and checks that two corner samples of thereference block of the reference block have been reconstructed. Inaddition, the processing circuitry checks that an additional sample ofthe reference block has been reconstructed. Then, the processingcircuitry reconstructs at least a sample of the current block based onreconstructed samples of the reference block that are retrieved from thereference sample memory.

In some embodiments, the processing circuitry checks that an additionalcorner sample of the reference block has been reconstructed. In anexample, the processing circuitry checks that a top left corner sampleand a bottom right corner sample of the reference block have beenreconstructed and then checks that a bottom left corner sample of thereference block has been reconstructed.

In some embodiments, the processing circuitry checks that a non-cornersample of the reference block has been reconstructed. In an embodiment,the processing circuitry checks that a sample located at about avertical center of the reference block has been reconstructed. Forexample, the processing circuitry checks that a bottom center sample ofthe reference block has been reconstructed.

In some embodiments, the processing circuitry determines whether enableconditions are met and then checks, when the enable conditions are met,that the non-corner sample of the reference block has beenreconstructed. In an example, the enable conditions include a firstcondition that the reference block is entirely on top of the currentblock and a second condition that a right edge of the reference block ison a right side of a left edge of the current block. In another example,the enable conditions include a first condition that the current blockis a lower child from a horizontal binary tree split, and a secondcondition that a combination of the current block and an upper childfrom the horizontal binary split is a middle partition of a verticalternary tree split.

In some embodiments, the processing circuitry checks that a samplelocated at a half block width left of a left edge of the current blockhas been reconstructed.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 2 is an illustration of exemplary intra prediction directions.

FIG. 3 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of acommunication system (500) in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 7 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 8 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 9 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 10 shows an example of intra block copy according to an embodimentof the disclosure.

FIGS. 11A-11D show examples of effective search ranges for the intrablock copy mode according to an embodiment of the disclosure.

FIG. 12 shows examples of collocated blocks according to someembodiments of the disclosure.

FIG. 13 shows examples for splits and coding orders.

FIG. 14 shows an example of split unit coding order in a coding treeunit.

FIG. 15 shows an example illustrating that additional checking locationsare needed according to some embodiments of the disclosure.

FIGS. 16A-16C show examples illustrating that additional checkinglocations are needed according to some embodiments of the disclosure.

FIG. 17 shows a flow chart outlining a process example according to someembodiment of the disclosure.

FIG. 18 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 4 illustrates a simplified block diagram of a communication system(400) according to an embodiment of the present disclosure. Thecommunication system (400) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (450). Forexample, the communication system (400) includes a first pair ofterminal devices (410) and (420) interconnected via the network (450).In the FIG. 4 example, the first pair of terminal devices (410) and(420) performs unidirectional transmission of data. For example, theterminal device (410) may code video data (e.g., a stream of videopictures that are captured by the terminal device (410)) fortransmission to the other terminal device (420) via the network (450).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (420) may receive the codedvideo data from the network (450), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (400) includes a secondpair of terminal devices (430) and (440) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (430) and (440)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (430) and (440) via the network (450). Eachterminal device of the terminal devices (430) and (440) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (430) and (440), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 4 example, the terminal devices (410), (420), (430) and(440) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (450) represents any number ofnetworks that convey coded video data among the terminal devices (410),(420), (430) and (440), including for example wireline (wired) and/orwireless communication networks. The communication network (450) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(450) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 5 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (513), that caninclude a video source (501), for example a digital camera, creating forexample a stream of video pictures (502) that are uncompressed. In anexample, the stream of video pictures (502) includes samples that aretaken by the digital camera. The stream of video pictures (502),depicted as a bold line to emphasize a high data volume when compared toencoded video data (504) (or coded video bitstreams), can be processedby an electronic device (520) that includes a video encoder (503)coupled to the video source (501). The video encoder (503) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (504) (or encoded video bitstream (504)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (502), can be stored on a streamingserver (505) for future use. One or more streaming client subsystems,such as client subsystems (506) and (508) in FIG. 5 can access thestreaming server (505) to retrieve copies (507) and (509) of the encodedvideo data (504). A client subsystem (506) can include a video decoder(510), for example, in an electronic device (530). The video decoder(510) decodes the incoming copy (507) of the encoded video data andcreates an outgoing stream of video pictures (511) that can be renderedon a display (512) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (504),(507), and (509) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (520) and (530) can includeother components (not shown). For example, the electronic device (520)can include a video decoder (not shown) and the electronic device (530)can include a video encoder (not shown) as well.

FIG. 6 shows a block diagram of a video decoder (610) according to anembodiment of the present disclosure. The video decoder (610) can beincluded in an electronic device (630). The electronic device (630) caninclude a receiver (631) (e.g., receiving circuitry). The video decoder(610) can be used in the place of the video decoder (510) in the FIG. 5example.

The receiver (631) may receive one or more coded video sequences to bedecoded by the video decoder (610); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (601), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (631) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (631) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (615) may be coupled inbetween the receiver (631) and an entropy decoder/parser (620) (“parser(620)” henceforth). In certain applications, the buffer memory (615) ispart of the video decoder (610). In others, it can be outside of thevideo decoder (610) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (610), forexample to combat network jitter, and in addition another buffer memory(615) inside the video decoder (610), for example to handle playouttiming. When the receiver (631) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (615) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (615) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (610).

The video decoder (610) may include the parser (620) to reconstructsymbols (621) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (610),and potentially information to control a rendering device such as arender device (612) (e.g., a display screen) that is not an integralpart of the electronic device (630) but can be coupled to the electronicdevice (630), as was shown in FIG. 6. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (620) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (620) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (620) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (620) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (615), so as tocreate symbols (621).

Reconstruction of the symbols (621) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (620). The flow of such subgroup control information between theparser (620) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (610)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (651). Thescaler/inverse transform unit (651) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (621) from the parser (620). The scaler/inversetransform unit (651) can output blocks comprising sample values, thatcan be input into aggregator (655).

In some cases, the output samples of the scaler/inverse transform (651)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (652). In some cases, the intra pictureprediction unit (652) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (658). The currentpicture buffer (658) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(655), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (652) has generated to the outputsample information as provided by the scaler/inverse transform unit(651).

In other cases, the output samples of the scaler/inverse transform unit(651) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (653) canaccess reference picture memory (657) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (621) pertaining to the block, these samples can beadded by the aggregator (655) to the output of the scaler/inversetransform unit (651) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (657) from where themotion compensation prediction unit (653) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (653) in the form of symbols (621) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (657) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (655) can be subject to variousloop filtering techniques in the loop filter unit (656). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (656) as symbols (621) from the parser (620), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (656) can be a sample stream that canbe output to the render device (612) as well as stored in the referencepicture memory (657) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (620)), the current picture buffer (658) can becomea part of the reference picture memory (657), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (610) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (631) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (610) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 7 shows a block diagram of a video encoder (703) according to anembodiment of the present disclosure. The video encoder (703) isincluded in an electronic device (720). The electronic device (720)includes a transmitter (740) (e.g., transmitting circuitry). The videoencoder (703) can be used in the place of the video encoder (503) in theFIG. 5 example.

The video encoder (703) may receive video samples from a video source(701) (that is not part of the electronic device (720) in the FIG. 7example) that may capture video image(s) to be coded by the videoencoder (703). In another example, the video source (701) is a part ofthe electronic device (720).

The video source (701) may provide the source video sequence to be codedby the video encoder (703) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any color space (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (701) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (701) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (703) may code andcompress the pictures of the source video sequence into a coded videosequence (743) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (750). In some embodiments, the controller(750) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (750) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (750) can be configured to have other suitablefunctions that pertain to the video encoder (703) optimized for acertain system design.

In some embodiments, the video encoder (703) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (730) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (733)embedded in the video encoder (703). The decoder (733) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (734). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (734) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (733) can be the same as of a“remote” decoder, such as the video decoder (610), which has alreadybeen described in detail above in conjunction with FIG. 6. Brieflyreferring also to FIG. 6, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (745) and the parser (620) can be lossless, the entropy decodingparts of the video decoder (610), including the buffer memory (615), andparser (620) may not be fully implemented in the local decoder (733).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (730) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (732) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (733) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (730). Operations of the coding engine (732) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 7), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (733) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (734). In this manner, the video encoder(703) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (735) may perform prediction searches for the codingengine (732). That is, for a new picture to be coded, the predictor(735) may search the reference picture memory (734) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(735) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (735), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (734).

The controller (750) may manage coding operations of the source coder(730), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (745). The entropy coder (745)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (740) may buffer the coded video sequence(s) as createdby the entropy coder (745) to prepare for transmission via acommunication channel (760), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(740) may merge coded video data from the video coder (703) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (750) may manage operation of the video encoder (703).During coding, the controller (750) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An intra picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (703) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (703) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (740) may transmit additional datawith the encoded video. The source coder (730) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 8 shows a diagram of a video encoder (803) according to anotherembodiment of the disclosure. The video encoder (803) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (803) is used in theplace of the video encoder (503) in the FIG. 5 example.

In an HEVC example, the video encoder (803) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (803) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (803) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(803) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (803) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 8 example, the video encoder (803) includes the interencoder (830), an intra encoder (822), a residue calculator (823), aswitch (826), a residue encoder (824), a general controller (821), andan entropy encoder (825) coupled together as shown in FIG. 8.

The inter encoder (830) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (822) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (822) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (821) is configured to determine general controldata and control other components of the video encoder (803) based onthe general control data. In an example, the general controller (821)determines the mode of the block, and provides a control signal to theswitch (826) based on the mode. For example, when the mode is the intramode, the general controller (821) controls the switch (826) to selectthe intra mode result for use by the residue calculator (823), andcontrols the entropy encoder (825) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(821) controls the switch (826) to select the inter prediction resultfor use by the residue calculator (823), and controls the entropyencoder (825) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (823) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (822) or the inter encoder (830). Theresidue encoder (824) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (824) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (803) also includes a residuedecoder (828). The residue decoder (828) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (822) and theinter encoder (830). For example, the inter encoder (830) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (822) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (825) is configured to format the bitstream toinclude the encoded block. The entropy encoder (825) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (825) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 9 shows a diagram of a video decoder (910) according to anotherembodiment of the disclosure. The video decoder (910) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (910) is used in the place of the videodecoder (510) in the FIG. 5 example.

In the FIG. 9 example, the video decoder (910) includes an entropydecoder (971), an inter decoder (980), a residue decoder (973), areconstruction module (974), and an intra decoder (972) coupled togetheras shown in FIG. 9.

The entropy decoder (971) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (972) or the inter decoder (980), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (980); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (972). The residual information can be subject to inversequantization and is provided to the residue decoder (973).

The inter decoder (980) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (972) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (973) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (973) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (971) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (974) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (973) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (503), (703), and (803), and thevideo decoders (510), (610), and (910) can be implemented using anysuitable technique. In an embodiment, the video encoders (503), (703),and (803), and the video decoders (510), (610), and (910) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (503), (703), and (703), and the videodecoders (510), (610), and (910) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide encoding/decoding techniques for intrapicture block compensation, especially techniques for determiningreference search range availability for intra picture block compensationwith flexible coding order.

Block based compensation can be used for inter prediction and intraprediction. For the inter prediction, block based compensation from adifferent picture is known as motion compensation. For intra prediction,block based compensation can also be done from a previouslyreconstructed area within the same picture. The block based compensationfrom reconstructed area within the same picture is referred to as intrapicture block compensation, current picture referencing (CPR) or intrablock copy (IBC). A displacement vector that indicates the offsetbetween the current block and the reference block in the same picture isreferred to as a block vector (or BV for short). Different from a motionvector in motion compensation, which can be at any value (positive ornegative, at either x or y direction), a block vector has a fewconstraints to ensure that the reference block is available and alreadyreconstructed. Also, in some examples, for parallel processingconsideration, some reference area that is tile boundary or wavefrontladder shape boundary is excluded.

The coding of a block vector could be either explicit or implicit. Inthe explicit mode (or referred to as advanced motion vector prediction(AMVP) mode in inter coding), the difference between a block vector andits predictor is signaled; in the implicit mode, the block vector isrecovered from a predictor (referred to as block vector predictor), in asimilar way as a motion vector in merge mode. The resolution of a blockvector, in some implementations, is restricted to integer positions; inother systems, the block vector is allowed to point to fractionalpositions.

In some examples, the use of intra block copy at block level, can besignaled using a block level flag that is referred to as an IBC flag. Inan embodiment, the IBC flag is signaled when the current block is notcoded in merge mode. In other examples, the use of the intra block copyat block level is signaled by a reference index approach. The currentpicture under decoding is then treated as a reference picture. In anexample, such a reference picture is put in the last position of a listof reference pictures. This special reference picture is also managedtogether with other temporal reference pictures in a buffer, such asdecoded picture buffer (DPB).

There are also some variations for intra block copy, such as flippedintra block copy (the reference block is flipped horizontally orvertically before used to predict current block), or line based intrablock copy (each compensation unit inside an M×N coding block is an M×1or 1×N line).

FIG. 10 shows an example of intra block copy according to an embodimentof the disclosure. Current picture (1000) is under decoding. The currentpicture (1000) includes a reconstructed area (1010) (doted area) andto-be-decoded area (1020) (white area). A current block (1030) is underreconstruction by a decoder. The current block (1030) can bereconstructed from a reference block (1040) that is in the reconstructedarea (1010). The position offset between the reference block (1040) andthe current block (1030) is referred to as a block vector (1050) (or BV(1050)).

In some examples (e.g., VVC), the search range of intra block copy modeis constrained to be within the current CTU. Then, the memoryrequirement to store reference samples for the intra block copy mode is1 (largest) CTU size of samples. In an example, the (largest) CTU has asize of 128×128 samples. The CTU is divided into four block regions thateach has a size of 64×64 samples, in some examples. Thus, in someembodiments, the total memory (e.g., cache memory with fast access speedthan a main storage) is able to store samples for a size of 128×128, andthe total memory includes an existing reference sample memory portion tostore reconstructed samples in the current block, such as a 64×64region, and additional memory portion to store samples of three otherregions of the size 64×64. Thus, in some examples, the effective searchrange of the intra block copy mode is extended to some part of the leftCTU while the total memory requirement for storing reference pixels arekept unchanged (e.g., 1 CTU size, 4 times of the 64×64 reference samplememory in total).

In some embodiments, an update process is performed to update the storedreference samples from the left CTU to the reconstructed samples fromthe current CTU. Specifically, in some examples, the update process isdone on a 64×64 luma sample basis. In an embodiment, for each of thefour 64×64 block regions in the CTU size memory, the reference samplesin the regions from the left CTU can be used to predict the coding blockin current CTU with CPR mode until any of the blocks in the same regionof the current CTU is being coded or has been coded.

FIGS. 11A-11D show examples of effective search ranges for the intrablock copy mode according to an embodiment of the disclosure. In someexamples, an encoder/decoder includes a cache memory that is able tostore samples of one CTU, such as 128×128 samples, and can be referredto as reference sample memory. In some embodiments, the reference samplememory is updated based on units of block regions. A CTU can include aplurality of block regions. Before a reconstruction of a block region, amemory space in the reference sample memory is allocated and reset tostore the reconstructed samples of the block region. In the FIGS.11A-11D examples, a block region for prediction has a size of 64×64samples. It is noted that the examples can be suitably modified forblock region of other suitable sizes.

Each of FIGS. 11A-11D shows a current CTU (1120) and a CTU to theimmediate left of the current CTU (hereinafter “left CTU”) (1110). Theleft CTU (1110) includes four block regions (1111)-(1114), and eachblock region has a sample size of 64×64 samples. The current CTU (1120)includes four block regions (1121)-(1124), and each block region has asample size of 64×64 samples. The current CTU (1120) is the CTU thatincludes a current block region (as shown with vertical stripe pattern)under reconstruction. The left CTU (1110) is the immediate neighbor onthe left side of the current CTU (1120). It is noted in FIGS. 11A-11D,the grey blocks are block regions that are already reconstructed, andthe white blocks are block regions that are to be reconstructed.

In FIG. 11A, the current block region under reconstruction is the blockregion (1121). The cache memory stores reconstructed samples in theblock regions (1112), (1113) and (1114), and the cache memory will beused to store reconstructed samples of the current block region (1121).In the FIG. 11A example, the effective search range for the currentblock region (1121) includes the block regions (1112), (1113) and (1114)in the left CTU (1110) with reconstructed samples stored in the cachememory. It is noted that, in an embodiment, the reconstructed samples ofthe block region (1111) are stored in a main memory (e.g., are copiedfrom the cache memory to the main memory before the reconstruction ofthe block region (1121)) that has a slower access speed than the cachememory.

In FIG. 11B, the current block region under reconstruction is the blockregion (1122). The cache memory stores reconstructed samples in theblock regions (1113), (1114) and (1121), and the cache memory will beused to store reconstructed samples of the current block region (1122).In the FIG. 11B example, the effective search range for the currentblock region (1122) includes the block regions (1113) and (1114) in theleft CTU (1110) and block region (1121) in the current CTU (1020) withreconstructed samples stored in the cache memory. It is noted that, inan embodiment, the reconstructed samples of the block region (1112) arestored in a main memory (e.g., are copied from the cache memory to themain memory before the reconstruction of the block region (1122)) thathas a slower access speed than the cache memory.

In FIG. 11C, the current block region under reconstruction is the blockregion (1123). The cache memory stores reconstructed samples in theblock regions (1114), (1121) and (1122), and the cache memory will beused to store reconstructed samples of the current block region (1123).In the FIG. 11C example, the effective search range for the currentblock (1123) includes the block region (1114) in the left CTU (1110) andblock regions (1121) and (1122) in the current CTU (1120) withreconstructed samples stored in the cache memory. It is noted that, inan embodiment, the reconstructed samples of the block region (1113) arestored in a main memory (e.g., are copied from the cache memory to themain memory before the reconstruction of the block region (1023)) thathas a slower access speed than the cache memory.

In FIG. 11D, the current block region under reconstruction is the blockregion (1124). The cache memory stores reconstructed samples in theblock regions (1121), (1122) and (1123), and the cache memory will beused to store reconstructed samples of the current block region (1124).In the FIG. 11D example, the effective search range for the currentblock region (1124) includes the blocks (1121), (1122) and (1123) in thecurrent CTU (1120) with reconstructed samples stored in the cachememory. It is noted that, in an embodiment, the reconstructed samples ofthe block region (1114) are stored in a main memory (e.g., are copiedfrom the cache memory to the main memory before the reconstruction ofthe block region (1124)) that has a slower access speed than the cachememory.

In some embodiments, the designated memory to store reference samples ofpreviously coded CUs for future intra block copy reference is referredas reference sample memory. In an example, such as VVC standard, one CTUsize of reference samples is considered as the designated memory size.In some examples, the cache memory has a total memory space for 1(largest) CTU size. The examples can be suitably adjusted for othersuitable CTU sizes. It is noted that the cache memory that is designatedto store reference samples of previously coded CUs for future intrablock copy reference is referred to as reference sample memory in someexamples.

According to an aspect of the disclosure, collocated blocks in thepresent disclosure refer to a pair of blocks that have the same sizes,one of the collocated blocks is in the previously coded CTU, the otherof the collocated blocks is in the current CTU, and one block in thepair is referred to as a collated block of the other block in the pair.Further, when the memory buffer size is designed to store a CTU of themaximum size (e.g., 128×128), then the previous CTU refers to the CTUthat has one CTU width luma sample offset to the left of current CTU inan example. In addition, these two collocated blocks have the samelocation offset values relative to the top left corner of their own CTU,respectively. Or in other words, collocated blocks are those two thathave the same y coordinate relative to the top left corner of a picture,but with a CTU width difference in x coordinates to one another in someexamples.

FIG. 12 shows examples of collocated blocks according to someembodiments of the disclosure. In the FIG. 12 example, a current CTU anda left CTU during decoding are shown. The area that has beenreconstructed is shown in grey color, and the area to be reconstructedis shown in white color. FIG. 12 shows three examples of referenceblocks in the left CTU for the current block in the intra block copymode during decoding. The three examples are shown as reference block 1,reference block 2 and reference block 3. FIG. 12 also shows thecollocated block 1 for the reference block 1, collocated block 2 for thereference block 2 and collocated block 3 for the reference block 3. Inthe FIG. 12 example, the reference sample memory size is a CTU size.Reconstructed samples of the current CTU and the left CTU are stored inthe reference sample memory in a complementary manner. When areconstructed sample of the current CTU is written to the referencesample memory, the reconstructed sample is written in the place of acollocated sample in the left CTU. In an example, for the referenceblock 3, because the collocated block 3 in the current CTU has not yetbeen reconstructed, thus the reference block 3 can be found from thereference sample memory. The reference sample memory still storessamples of the reference block 3 from the left CTU and can be accessedwith fast speed to retrieve the samples of the reference block 3, andthe reference block 3 can be used to reconstruct the current block inthe intra block copy mode in an example.

In another example, for the reference block 1, the collocated block 1 inthe current CTU has been reconstructed completed, thus the referencesample memory stores samples of the collocated block 1, and the samplesof the reference block 1 have been stored in, for example, an off-chipstorage that has relative high delay compared to the reference samplememory. Thus, in an example, the reference block 1 cannot be found inthe reference sample memory, and the reference block 1 cannot be used toreconstruct the current block in the intra block copy mode in anexample.

Similarly, in another example, for the reference block 2, even if thecollocated block 2 in the current CTU has not yet been reconstructed,because the 64×64 block region that includes the collocated blocks 2 isconsidered as a whole in a memory update example, then the referenceblock 2 is not a valid reference block for reconstructing the currentblock in the intra block copy mode.

Generally, in the intra block copy mode, for a reference block in thepreviously decoded CTU, when the collocated block in the current CTU hasnot yet been reconstructed, then samples of the reference block areavailable in the reference sample memory, and the reference samplememory can be accessed to retrieve the samples of the reference block touse as reference for reconstruction in the intra block copy mode.

It is noted that, in the above examples, the top left corner sample ofthe collocated block in the current CTU, which is also referred to asthe collocated sample of the top left corner of the reference block, ischecked. When the collocated sample in the current CTU has not yet beenreconstructed, the rest of samples for the reference block will all beavailable for use as reference in the intra block copy.

In some embodiments, a CTU may be divided into block regions todetermine valid reference block regions. For example, a CTU of 128×128is divided into four 64×64 block regions. In an example, for thereference block 2, even if the collocated block 2 in the current CTU hasnot yet been reconstructed, the reference block 2 may not become a validreference block if the entire 64×64 block region (1201) of thecollocated block 2 is considered as a whole. For example, by checkingthe top left corner (1202) of the 64×64 block region (1201) (top-right64×64 region of current CTU) where the collocated block 2 belongs to,that top left corner (1202) is considered being reconstructed thereforethe entire of the 64×64 block region (1203) where reference block 2belongs to cannot be used as reference block region.

When reference sample memory size is larger than the CTU size, more than1 CTU to the left may be used to store reference samples for intra blockcopy. For example, when the CTU size is 64×64 while the reference memorysize is 128×128, in addition to current CTU, 3 left CTUs may beconsidered as the valid reference area for intra block copy.

It is also noted that, in the above examples, the memory size of thereference sample memory is the size of one CTU, then the previouslydecoded CTU means the CTU immediate to the left of current CTU.

According to an aspect of the disclosure, the memory size of thereference sample memory can be larger than the size of one CTU.

According to some aspects of the disclosure, for a valid search range,the bitstream conformance requires the luma block vector mvL to obey thecertain constraints. In an example, a current CTB is a luma CTBincluding a plurality of luma samples and a block vector mvL satisfiesthe following constraints for bitstream conformance.

In some examples, first constraints are used to make sure that thereference block for the current block has to be reconstructed. When thereference block has a rectangular shape, a reference block availabilitychecking process can be implemented to check whether a top left sampleand a bottom right sample of the reference block are reconstructed. Whenboth the top left sample and the bottom right sample of the referenceblock are reconstructed, the reference block is determined to have beenreconstructed.

For example, a reconstructed top left sample of the reference blockshould be available. In some examples, a derivation process for blockavailability can be invoked, the derivation process can receive acurrent luma location and a neighboring luma position as inputs, andgenerate an output that indicates whether a sample at the neighboringluma position has been reconstructed. For example, when the output isTRUE, the sample at the input position has been reconstructed; and whenthe output is FALSE, the sample at the input position hasn't beenreconstructed yet.

Generally, the current luma position is set to (xCb, yCb), which is theposition of the top left sample of the current block. Further, mvLdenotes block vector, mvL[0] denotes the x component and mvL[1] denotesthe y component of the block vector. In some examples, the x componentand y component are stored in 1/16 inter sample accuracy, thus the xcomponent and the y component can have 4-bit for fractional parts of apixel. Then, to get the inter part, the x component and y component canbe right shift by 4. The current luma location (xCurr, yCurr) is set tobe the top left sample of the current block (xCb, yCb), the neighboringluma location can be represented by (xCb+(mvL[0]>>4), yCb+(mvL[1]>>4))which is the position of the top left sample of the reference block. Inan example, a derivation process for reference block availability isinvoked, the positon of the top left sample of the reference block isused as an input, when an output is equal to TRUE, the top left sampleof the reference block is reconstructed. The availability check of thetop left sample of the reference block is referred to as check-A.

Similarly, the reconstructed bottom right sample of the reference blockshould be available. In some examples, a derivation process for blockavailability can be invoked, and the input to the derivation processincludes the position of the bottom right sample of the reference block.For example, the current luma positon is set to be (xCb, yCb), and widthof the current block and the reference block is denoted by cbWidth, theheight of the current block and the reference block is denoted bycbHeight. Then, the position of the bottom right sample of the referenceblock is (xCb+(mvL[0]>>4)+cbWidth−1, yCb+(mvL[1]>>4)+cbHeight−1). Theposition of the bottom right sample is input to the derivation processfor block availability, when the output is TRUE, the bottom right sampleof the reference block is reconstructed. The availability check of thebottom right sample is referred to as check-B.

In some examples, second constraints ensure that the reference block isto the left and/or above of the current block and does not overlap withthe current block. The second constraints can also include at least oneof the following two conditions: 1) a value of (mvL[0] >>4)+cbWidth isless than or equal to 0, which indicates that the reference block is tothe left of the current block and does not overlap with the currentblock; 2) a value of (mvL[1]>>4)+cbHeight is less than or equal to 0,which indicates that the reference block is above the current block anddoes not overlap with the current block. In an example, a check isperformed according to the second constraints, and is referred to ascheck-C.

The third constraints ensure the reference block is in an appropriatesearch range. In some examples, the third constrains can include thatthe following conditions are satisfied by the block vector mvL:

(yCb+(mvL[1]>>4))>>Ctb Log 2SizeY=yCb>>Ctb Log 2SizeY  (Eq. 1)

(yCb+(mvL[1]>>4+cbHeight−1)>>Ctb Log 2SizeY=yCb>>Ctb Log 2SizeY  (Eq. 2)

(xCb+(mvL[0]>>4))>>Ctb Log 2SizeY>=(xCb>>Ctb Log 2SizeY)—(1<<((7−Ctb Log2SizeY)<<1)))+Min(1,7—Ctb Log 2SizeY)  (Eq. 3)

(xCb+(mvL[0]>>4)+cbWidth−1)>>Ctb Log 2SizeY<=(xCb>>Ctb Log 2SizeY)  (Eq.4)

where the parameters CtbLog2SizeY denotes the CTB size (e.g., height orwidth) in log 2 form. For example, when the CTB height is 128 samples,CtbLog2SizeY is 7. (Eq. 1) and (Eq. 2) specify that a CTB including thereference block is in a same CTB row as the current CTB (i.e., thepreviously reconstructed CTB is in a same row as the current CTB whenthe reference block is in the previously reconstructed CTB). (Eq. 3) and(Eq. 4) specify that the CTB including the reference block is either ina left CTB column of the current CTB or a same CTB column as the currentCTB. The conditions as described by (Eq. 1)-(Eq. 4) specify that the CTBincluding the reference block is either the current CTB, or a leftneighbor, such as the previously reconstructed CTB, of the current CTB.

In an example, a check that is performed according to (Eq. 1) isreferred to as check-D; a check that is performed according to (Eq. 2)is referred to as check-E; a check that is performed according to (Eq.3) is referred to as check-F; a check that is performed according to(Eq. 2) is referred to as check-G.

The fourth constraints ensure the reference block is stored in thereference sample memory, in other words, the collocated block of thereference block has not been reconstructed. In some examples, the fourthconstraints can include following conditions: when the reference blockis in the left neighbor of the current CTB, a collocated region for thereference block is not reconstructed (i.e., no samples in the collocatedregion have been reconstructed). Further, the collocated region for thereference block is in the current CTB.

In an example, the above conditions can be specified as below: when(xCb+(mvL[0]>>4))>>CtbLog2SizeY is equal to (xCb>>CtbLog2SizeY)−1, andCtbLog2SizeY is 7, the derivation process for reference blockavailability is invoked. The input for the current luma location (xCurr,yCurr) is set to be (xCb, yCb) and the input for the neighboring lumalocation is(((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY−1),((yCb+(mvL[1]>>4))>>(CtbLog2SizeY− 1))<<(CtbLog2SizeY− 1)). When anoutput of the derivation process is FALSE, the collocated region has notbeen reconstructed. In an example, the check of the collocated region isreferred to as check-H.

Also, the luma location (((xCb+(mvL[0]>>4)+CtbSizeY)>>(CtbLog2SizeY−1))<<(CtbLog2SizeY− 1), ((yCb+(mvL[1]>>4))>>(CtbLog2SizeY−1))<<(CtbLog2SizeY− 1)) shall not be equal to (xCb, yCb). In an example,the inequality check is referred to as check-I.

According to some aspects of the disclosure, flexible coding order canbe used in some coding techniques. In some embodiments, a CTU isrecursively partitioned by quad-tree structure, binary tree structure ortriple tree structure. The units in the partitioning process, which arefurther split into two, three, or four units are named split units(SUs). Usually the coding order of a split unit is from left to rightand from above to bottom because of z scanning order of quad treestructure and raster scan of CTUs in a picture. However, normal left toright coding order is more beneficial to left inclined features thanright inclined features. Not limited to intra prediction, even in interprediction blocks with right inclined features cannot find similarmotion information from left and above neighborhood.

In some examples, a technique that is referenced to as split unit codingorder (SUCO) can be used. SUCO enables more flexible coding order, suchas left to right (L2R) and right to left (R2L), to allow intraprediction from right reference pixels and inter prediction with rightmotion vector predictors. In some examples, if a split unit (SU) ispartitioned vertically, a flag is signaled to indicate L2R or R2L codingorder. Further, if a SU is partitioned by quad tree structure, a flag isshared for above two units and bottom two units. If no flag is signaledfor the coding order of a SU, the following coding orders of that SUimplicitly inherit from previous level SU.

FIG. 13 shows examples for splits and coding orders. For example, asplit unit 1310 can be partitioned according to binary tree (BT)structure, triple tree (TT) structure, and quad-tree (QT) structure, andcan be suitable coded in a left to right (L2R) order or a right to left(R2L) order.

For example, the split unit 1310 is vertically partitioned into units1321 and 1322 according to BT structure. The units 1321 and 1322 can becoded in an L2R order or an R2L order. The split unit 1310 ishorizontally partitioned into units 1331 and 1332 according to BTstructure. The units 1331 and 1332 are coded generally in an above tobottom order.

In another example, the split unit 1310 is vertically partitioned intounits 1341-1343 according to TT structure. The units 1341-1343 can becoded in an L2R order or an R2L order. The split unit 1310 ishorizontally partitioned into units 1351-1352. The units 1351-1353 arecoded generally in an above to bottom order.

In another example, the split unit 1310 is partitioned into units1361-1364 according to QT structure. For L2R order, the units 1361-1364can be coded following 1361, 1362, 1363 and 1364. For R2L order, theunits 1361-1364 can be coded following 1362, 1361, 1364 and 1363.

FIG. 14 shows an example of SUCO in a CTU. In the FIG. 14 examples, aCTU 1410 is partitioned according to a tree structure 1450. The CTU 1410is also referred to as a unit S1. The unit S1 is partitioned into unitsS21-S24 according to QT structure, and coded in the R2L order. The unitS21 is horizontally partitioned into units S31-S32 according to BTstructure. The unit S31 is vertically partitioned into units S41-S43according to TT structure, and coded in the R2L order. The unit S32 isvertically partitioned into units S44-S45 according to BT structure andcoded in the L2R order. The unit S45 is horizontally partitioned intounits S51-S52 according to BT structure. The unit S52 is verticallypartitioned into units S61-S62 according to BT structure and coded inthe L2R order. In the FIG. 14 example, when a unit is furtherpartitioned, the unit can be referred to as a split unit (SU). When aunit is not further partitioned, the unit can be referred to as a leafCU.

In the FIG. 14 example, due to the flexible coding order in SU level,the neighboring availability of a leaf CU become more diverse thancommon left and above neighbors in HEVC. For example, there are fouravailability cases if only left and right neighboring blocks areconsidered. Specifically, for the first case that is referred to asLR_10, the left neighboring block is available and the right neighboringblock is not available; for the second case that is referred to asLR_01, the left neighboring block is not available and the rightneighboring block is available; for the third case that is referred toas LR_11, both of the left neighboring block and the right neighboringblock are available; and for the fourth case that is referred to asLR_00, both of the left neighboring block and the right neighboringblock are not available. The above block is always available unless thecurrent CU lies on the top boundary of a slice. Availability of theabove left or above right corner block depends on the corresponding leftor right neighbor availability.

Usually, when the block coding order is from left to right and from topto bottom, the above and left areas of the current coding block can bethe reference area with already reconstructed samples for intra pictureblock compensation. When SUCO is used, the coding order and neighboringreference sample availability become more complex. Aspects of thedisclosure provide techniques to specify the available search range forintra block copy.

The proposed methods may be used separately or combined in any order.Further, each of the methods (or embodiments), encoder, and decoder maybe implemented by processing circuitry (e.g., one or more processors orone or more integrated circuits). In one example, the one or moreprocessors execute a program that is stored in a non-transitorycomputer-readable medium. In the following description, the term blockmay be interpreted as a prediction block, a coding block, or a codingunit, i.e. CU.

In the examples that the block coding order is from left to right andfrom top to bottom, when a reference block's top left corner and bottomright corner are valid for intra block copy (meaning samples at thesetwo locations have been reconstructed and conform to the restrictionsfor intra block copy, for example, inside the same tile/slice of thecurrent coding block), then all samples of the reference block have beenreconstructed and conform to the restrictions for intra block copy (forexample, inside the same tile/slice of the current coding block) and thereference block is a valid block for intra block copy.

However, when SUCO is used, checking only the top left corner and thebottom right corner of a potential reference block is not enough, morevalid checking points are used to determine the sample availability ofpotential reference block.

In the following description, some positions of the current coding blockare referred, and some positions of a (potential) reference block arereferred. For example, top left corner of current coding block isreferred to as (Cur_TL_x, Cur_TL_y); the top-right corner of currentcoding block is referred to as (Cur_TR_x, Cur_TR_y); the bottom-leftcorner of current coding block is referred to as (Cur_BL_x, Cur_BL_y);the bottom right corner of current coding block is referred to as(Cur_BR_x, Cur_BR_y). The width of the current coding block is referredto as cbWidth and the height of the current coding block is referred toas cbHeight. The top left corner of reference block is referred to as(Ref_TL_x, Ref_TL_y); the top-right corner of reference block isreferred to as (Ref_TR_x, Ref_TR_y); the bottom-left corner of referenceblock is referred to as (Ref_BL_x, Ref_BL_y); the bottom right corner ofreference block is referred to as (Ref_BR_x, Ref_BR_y).

According to an aspect of the disclosure, when SUCO is used, for acurrent coding block, the right neighboring blocks may be coded prior tothe left neighboring blocks. Thus, in some examples, even though bothtop left and bottom right corners of a reference block are valid, theentire block may still be an invalid reference block for intra blockcopy.

FIG. 15 shows an example illustrating that additional checking locationsare needed according to some embodiments of the disclosure. In the FIG.15 example, a CTU (1500) is partitioned into coding blocks (1510),(1520), (1530), (1540), (1550) and (1560). When SUCO is used, the codingblocks can be coded in an order of (1510), (1530), (1560), (1550),(1540) and (1520) in an example. In an example, at the time of decoding(or encoding) the coding block (1560), the coding block (1560) is thecurrent coding block (shown with vertical stripes), the coding blocks(1510) and (1530) have been reconstructed (shown with grey color), andthe coding blocks (1550), (1540) and (1520) haven't been reconstructed.

In the FIG. 15 example, at the time to code the current coding block(1560), a block vector points to a (potential) reference block (1590).Then, the reference block (1590) is checked. The top left and the bottomright corners of the reference block (1590) have been reconstructed.Thus, when only top left and the bottom right corners are checked, awrong decision that the reference block (1590) is valid as a referenceblock for the current coding block (1560) may be made. However, as shownin FIG. 15, some portions of the reference block (1590) haven't beenreconstructed, and the reference block (1590) is actually invalid.

To avoid using invalid reference block, or in another word, to make surea selected reference block by the block vector is valid, in addition tothe availability checks of top left and bottom right corners of thereference block, the reference block's bottom left corner, that isreferred to as (Ref_BL_x, Ref_BL_y) is also checked to make sure thesamples at that corner is valid for intra block copy reference (e.g.,samples there should have been reconstructed, within the same tile/sliceof current block, etc.). In the FIG. 15 example, when the bottom leftcorner is checked, the reference block (1590) can be determined to beinvalid reference block.

According to another aspect of the disclosure, when SUCO is used, evenwhen all four corners of a reference block have been reconstructed priorto the current coding block, the reference block can be invalid in someexamples.

FIGS. 16A-16C show examples illustrating that additional checkinglocations are needed according to some embodiments of the disclosure. Inthe FIGS. 16A-16C example, a CTU (1600) is partitioned into codingblocks (1610), (1620), (1630), (1640), (1650) and (1660). When SUCO isused, the coding blocks can be coded in an order of (1610), (1620),(1630), (1670), (1650), (1660) and (1640) in an example. In an example,at the time of decoding (or encoding) the coding block (1660), thecoding block (1660) is the current coding block (shown with verticalstripes), the coding blocks (1610), (1620), (1630), (1670) and (1650)have been reconstructed (shown with grey color), and the coding blocks(1640) hasn't been reconstructed.

In the FIG. 16A example, at the time to code the current coding block(1660), a block vector points to a (potential) reference block (1690A).Then, the reference block (1690A) is checked. The top left and thebottom right corners of the reference block (1690A) have beenreconstructed. Thus, when only top left and the bottom right corners arechecked, a wrong decision that the reference block (1690A) is valid as areference block for the current coding block (1660) may be made.However, as shown in FIG. 16A, some portions of the reference block(1690A) haven't been reconstructed, and the reference block (1690A) isactually invalid.

Similarly, in the FIG. 16B example, at the time to code the currentcoding block (1660), a block vector points to a (potential) referenceblock (1690B). Then, the reference block (1690B) is checked. The topleft and the bottom right corners of the reference block (1690B) havebeen reconstructed. Thus, when only top left and the bottom rightcorners are checked, a wrong decision that the reference block (1690B)is valid as a reference block for the current coding block (1660) may bemade. However, as shown in FIG. 16B, some portions of the referenceblock (1690B) haven't been reconstructed, and the reference block(1690B) is actually invalid.

Also, in the FIG. 16C example, at the time to code the current codingblock (1660), a block vector points to a (potential) reference block(1690C). Then, the reference block (1690C) is checked. The top left andthe bottom right corners of the reference block (1690C) have beenreconstructed. Thus, when only top left and the bottom right corners arechecked, a wrong decision that the reference block (1690C) is valid as areference block for the current coding block (1660) may be made.However, as shown in FIG. 16C, some portions of the reference block(1690C) haven't been reconstructed, and the reference block (1690C) isactually invalid.

To avoid using invalid reference block, or in another word, to make surea selected reference block by the block vector is valid, in addition tothe availability checks of top left and bottom right corners, a point ona center line of the reference block can be checked. In the FIGS.16A-16C example, according to some embodiments, samples located at abouta vertical center line (1680) (e.g., x=Ref_BL_x+cbWidth/2) of thereference block can be checked. In an example, the reference block'sbottom line center, that can be referred to as (Ref_BL_x+cbWidth/2,Ref_BL_y), can be checked in addition and make sure that a sample atthat location is valid for intra block copy reference (e.g., samples atthe location should have been reconstructed, within the same tile/sliceof current block, etc.).

According to an aspect of the disclosure, the checking on the additionalpoint(s) (besides the top left and the bottom right corners) for theavailability condition check may be conditionally used. Thus, in someexamples, only under certain circumstances, for example, the invalidreference blocks shown in FIGS. 16A-16C, will be possible, and then theadditional point(s) may need to be checked.

In an embodiment, the conditions to enable the availability check of theadditional point(s) can be: the reference block is entirely on top ofcurrent coding block, and the x component of the right edge of thereference block is larger than or equal to the x component of the leftedge of the current coding block.

In another embodiment, the current coding block is a lower childpartition from a horizontal BT split. A combination of the current blocktogether with the upper child partition of the horizontal BT (belongingto the same parent node) is the middle partition of a vertical ternaryTT split. The coding order for the TT split is from right to left. FIGS.16A-16C show examples of such situation for the current coding block. Inanother embodiment, the additional checking point of the reference blockavailability check can be changed from position (Ref_BL_x+cbWidth/2,Ref_BL_y) another position: (Cur_TL_x−cbWidth/2, Ref_BR_y), which islocated left at about half block width of the left edge of the currentcoding block, and is shown by (1681) in FIG. 16A.

According to some aspects of the disclosure, when SUCO is used, for avalid search range, the bitstream conformance requires the luma blockvector mvL to obey the certain constraints. In an example, a current CTBis a luma CTB including a plurality of luma samples and a block vectormvL satisfies the following constraints for bitstream conformance whenSUCO is used, and mvL represents the block vector in 1/16 resolution.

In some examples, first constraints are used to make sure that thereference block for the current block has been reconstructed. When thereference block has a rectangular shape, a reference block availabilitychecking process can be implemented to check whether a top left sample,a bottom right sample of the reference block are reconstructed, andadditional point(s) when SUCO is used. When SUCO is not used, if the topleft sample and the bottom right sample of the reference block arereconstructed, the reference block is determined to have beenreconstructed. When SUCO is used, if the top left sample, the bottomright sample of the reference block and the additional point(s) arereconstructed, the reference block is determined to have beenreconstructed.

In some implementation examples, check-A and check-B are performed torespectively check the top left sample and the bottom right sample ofthe reference block.

In addition, in an embodiment, when SUCO is used, the reconstructedbottom left sample of the reference block should be available, to avoidinvalid reference blocks as shown in FIG. 15. In some examples, aderivation process for block availability can be invoked, and the inputto the derivation process includes the position of the bottom leftsample of the reference block. For example, the current luma positon isset to be (xCb, yCb), and width of the current block and the referenceblock is denoted by cbWidth, the height of the current block and thereference block is denoted by cbHeight. Then, the position of the bottomleft sample of the reference block is (xCb+(mvL[0]>>4),yCb+(mvL[1]>>4)+cbHeight−1). The position of the bottom left sample isinput to the derivation process for block availability, when the outputis TRUE, the bottom right sample of the reference block isreconstructed.

In another embodiment, when SUCO is used, the reconstructed verticalmiddle sample(s) of the reference block should be available, to avoidinvalid reference blocks as shown in FIGS. 16A-16C. In some examples, aderivation process for block availability can be invoked, and the inputto the derivation process includes the position of the bottom leftsample of the reference block. For example, the current luma positon isset to be (xCb, yCb), and width of the current block and the referenceblock is denoted by cbWidth, the height of the current block and thereference block is denoted by cbHeight. Then, the position of the bottomcenter sample of the reference block is (xCb+(mvL[0]>>4+cbWidth/2),yCb+(mvL[1]>>4)+cbHeight−1). The position of the bottom center sample isinput to the derivation process for block availability, when the outputis TRUE, the bottom right sample of the reference block isreconstructed.

In some examples, check-C is modified to ensure that the reference blockis to the left and/or above of the current block and/or to the right ofthe current block, does not overlap with the current block. Theconstraints for check-C can also include at least one of the followingthree conditions: 1) the value of (mvL[0]>>4)+cbWidth is less than orequal to 0, which indicates that the reference block is to the left ofthe current block and does not overlap with the current block; 2) thevalue of (mvL[1]>>4)+cbHeight is less than or equal to 0, whichindicates that the reference block is above the current block and doesnot overlap with the current block; and 3) the value of (mvL[0]>>4) isgreater than or equal to cbWidth, which indicates that the referenceblock is to the right of the current block and does not overlap with thecurrent block.

Further, check-D, check-E, check-F, check-G, check-H and check-I can besimilarly performed as described.

FIG. 17 shows a flow chart outlining a process (1700) according to anembodiment of the disclosure. The process (1700) can be used in thereconstruction of a block, so to generate a prediction block for theblock under reconstruction. In various embodiments, the process (1700)are executed by processing circuitry, such as the processing circuitryin the terminal devices (410), (420), (430) and (440), the processingcircuitry that performs functions of the video encoder (503), theprocessing circuitry that performs functions of the video decoder (510),the processing circuitry that performs functions of the video decoder(610), the processing circuitry that performs functions of the videoencoder (703), and the like. In some embodiments, the process (1700) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1700). The process starts at (S1701) and proceeds to(S1710).

At (S1710), prediction information of a current block is decoded from acoded video bitstream. The prediction information is indicative of intrablock copy mode. The current block is one of a plurality of codingblocks in a CTB with a right to left coding order being allowed withinthe CTB. For example, SUCO is used to enable flexible coding order inthe CTB.

At (S1720), a block vector is determined. The block vector points to areference block in a same picture as the current block.

At (S1730), two corner samples of the reference block are checked to beavailable. For example, check-A is performed to make sure that the topleft corner sample has been reconstructed and check-B is performed tomake sure that the bottom right corner sample has been reconstructed.

At (S1740), additional check is performed on a sample in addition to thetwo corner samples to make sure the sample has been reconstructed. In anexample, the sample of additional check is a corner sample, such as abottom left corner sample. In some examples, the sample of additionalcheck is a non-corner sample. In an example, the sample of additionalcheck is located about a vertical center of the reference block, such asbottom center sample of the reference block.

At (S1750), samples of the current block are reconstructed based on thereconstructed samples of the reference block. Then, the process proceedsto (S1799) and terminates.

It is noted that additional checks are performed to ensure that thereference block is a valid block, such as check-C, check-D, check-E,check-F, check-G, check-H, check-I and the like.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 18 shows a computersystem (1800) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 18 for computer system (1800) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1800).

Computer system (1800) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1801), mouse (1802), trackpad (1803), touchscreen (1810), data-glove (not shown), joystick (1805), microphone(1806), scanner (1807), camera (1808).

Computer system (1800) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1810), data-glove (not shown), or joystick (1805), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1809), headphones(not depicted)), visual output devices (such as screens (1810) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1800) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1820) with CD/DVD or the like media (1821), thumb-drive (1822),removable hard drive or solid state drive (1823), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1800) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1849) (such as, for example USB ports of thecomputer system (1800)); others are commonly integrated into the core ofthe computer system (1800) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1800) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1840) of thecomputer system (1800).

The core (1840) can include one or more Central Processing Units (CPU)(1841), Graphics Processing Units (GPU) (1842), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1843), hardware accelerators for certain tasks (1844), and so forth.These devices, along with Read-only memory (ROM) (1845), Random-accessmemory (1846), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1847), may be connectedthrough a system bus (1848). In some computer systems, the system bus(1848) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1848),or through a peripheral bus (1849). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1841), GPUs (1842), FPGAs (1843), and accelerators (1844) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1845) or RAM (1846). Transitional data can be also be stored in RAM(1846), whereas permanent data can be stored for example, in theinternal mass storage (1847). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1841), GPU (1842), massstorage (1847), ROM (1845), RAM (1846), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1800), and specifically the core (1840) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1840) that are of non-transitorynature, such as core-internal mass storage (1847) or ROM (1845). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1840). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1840) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1846) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1844)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video encoding, comprising:determining, by a processor, a block vector that points to a referenceblock in a same picture as a current block in an intra block copy mode,the current block being one of a plurality of coding blocks in a codingtree block (CTB) with a right to left coding order being allowed withinthe CTB; checking, by the processor, that two corner samples of thereference block have been reconstructed based on first outputs from aderivation process for block availability, the derivation process forblock availability generating the first outputs in response to positionsof the two corner samples; checking, by the processor, that a non cornersample of the reference block has been reconstructed based on a secondoutput from the derivation process for block availability, thederivation process for block availability generating the second outputin response to a position of the non corner sample of the referenceblock; and encoding, by the processor, the current block based onreconstructed samples of the reference block after a determination thatthe two corner samples of the reference block and the non corner sampleof the reference block have been reconstructed.
 2. The method of claim1, wherein the checking the non corner sample further comprises:checking that a sample located at about a vertical center of thereference block has been reconstructed based on the second output fromthe derivation process for block availability, the derivation processfor block availability generating the second output in response to theposition of the sample located at about the vertical center of thereference block.
 3. The method of claim 2, wherein the checking thesample located at about the vertical center further comprises: checkingthat a bottom center sample of the reference block has beenreconstructed based on the second output from the derivation process forblock availability, the derivation process for block availabilitygenerating the second output in response to the position of the bottomcenter sample of the reference block.
 4. The method of claim 1, furthercomprising: determining whether enable conditions are met; and whereinthe checking the non corner sample further includes checking, when theenable conditions are met, that the non corner sample of the referenceblock has been reconstructed.
 5. The method of claim 4, wherein theenable conditions include the reference block being entirely on top ofthe current block; and a right edge of the reference block being on aright side of a left edge of the current block.
 6. The method of claim4, wherein the enable conditions include the current block being a lowerchild from a horizontal binary tree split; and a combination of thecurrent block and an upper child from the horizontal binary tree splitbeing a middle partition of a vertical ternary tree split.
 7. The methodof claim 1, wherein the checking the non corner sample furthercomprises: checking that a sample located at a half block width left ofa left edge of the current block has been reconstructed based on thesecond output from the derivation process for block availability, thederivation process for block availability generating the second outputin response to the position of the sample at the half block width leftof the left edge of the current block.
 8. An apparatus for videodecoding, comprising: processing circuitry configured to: determine ablock vector that points to a reference block in a same picture as acurrent block in an intra block copy mode, the current block being oneof a plurality of coding blocks in a coding tree block (CTB) with aright to left coding order being allowed within the CTB; check that twocorner samples of the reference block of the reference block have beenreconstructed based on first outputs from a derivation process for blockavailability, the derivation process for block availability generatingthe first outputs in response to positions of the two corner samples;check that a non corner sample of the reference block has beenreconstructed based on a second output from the derivation process forblock availability, the derivation process for block availabilitygenerating the second output in response to a position of the non cornersample of the reference block; and encode the current block based onreconstructed samples of the reference block after a determination thatthe two corner samples of the reference block and the non corner sampleof the reference block have been reconstructed.
 9. The apparatus ofclaim 8, wherein the processing circuitry is configured to: check that asample located at about a vertical center of the reference block hasbeen reconstructed based on the second output from the derivationprocess for block availability, the derivation process for blockavailability generating the second output in response to the position ofthe sample located at about the vertical center of the reference block.10. The apparatus of claim 9, wherein the processing circuitry isconfigured to: check that a bottom center sample of the reference blockhas been reconstructed based on the second output from the derivationprocess for block availability, the derivation process for blockavailability generating the second output in response to the position ofthe bottom center sample of the reference block.
 11. The apparatus ofclaim 8, wherein the processing circuitry is configured to: determinewhether enable conditions are met; and check, when the enable conditionsare met, that the non corner sample of the reference block has beenreconstructed.
 12. The apparatus of claim 11, wherein the enableconditions include the reference block being entirely on top of thecurrent block; and a right edge of the reference block being on a rightside of a left edge of the current block.
 13. The apparatus of claim 11,wherein the enable conditions include the current block being a lowerchild from a horizontal binary tree split; and a combination of thecurrent block and an upper child from the horizontal binary tree splitbeing a middle partition of a vertical ternary tree split.
 14. Theapparatus of claim 8, wherein the processing circuitry is configured to:check that a sample located at a half block width left of a left edge ofthe current block has been reconstructed based on the second output fromthe derivation process for block availability, the derivation processfor block availability generating the second output in response to theposition of the sample at the half block width left of the left edge ofthe current block.
 15. A non-transitory computer-readable storage mediumstoring instructions which when executed by a processor cause theprocessor to perform: determining a block vector that points to areference block in a same picture as a current block in an intra blockcopy mode, the current block being one of a plurality of coding blocksin a coding tree block (CTB) with a right to left coding order beingallowed within the CTB; checking that two corner samples of thereference block have been reconstructed based on first outputs from aderivation process for block availability, the derivation process forblock availability generating the first outputs in response to positionsof the two corner samples; checking that a non corner sample of thereference block has been reconstructed based on a second output from thederivation process for block availability, the derivation process forblock availability generating the second output in response to aposition of the non corner sample of the reference block; and encodingthe current block based on reconstructed samples of the reference blockafter a determination that the two corner samples of the reference blockand the non corner sample of the reference block have beenreconstructed.
 16. The non-transitory computer-readable storage mediumof claim 15, wherein the checking the non corner sample furthercomprises: checking that a sample located at about a vertical center ofthe reference block has been reconstructed based on the second outputfrom the derivation process for block availability, the derivationprocess for block availability generating the second output in responseto the position of the sample located at about the vertical center ofthe reference block.
 17. The non-transitory computer-readable storagemedium of claim 16, wherein the checking the sample located at about thevertical center further comprises: checking that a bottom center sampleof the reference block has been reconstructed based on the second outputfrom the derivation process for block availability, the derivationprocess for block availability generating the second output in responseto the position of the bottom center sample of the reference block. 18.The non-transitory computer-readable storage medium of claim 15, whereinthe instructions further cause the processor to perform: determiningwhether enable conditions are met; and wherein the checking the noncorner sample further includes checking, when the enable conditions aremet, that the non corner sample of the reference block has beenreconstructed.
 19. The non-transitory computer-readable storage mediumof claim 18, wherein the enable conditions include the reference blockbeing entirely on top of the current block; and a right edge of thereference block being on a right side of a left edge of the currentblock.
 20. The non-transitory computer-readable storage medium of claim18, wherein the enable conditions include the current block being alower child from a horizontal binary tree split; and a combination ofthe current block and an upper child from the horizontal binary splitbeing a middle partition of a vertical ternary tree split.